WHY would I be pursing this project ????,....perhaps just a bit of my history.
A few years ago I experienced some problems with the pulling power of some of the steam engines I had. And in my reading of numerous forums I saw where other folks had experienced the same with some of their steamers. So like some have suggested why not double-head them, or add some sort of other pusher,...perhaps a diesel engine one.
That's what I did back in 2021,..
Pusher/Helper
Back to the pusher/helper idea.
I had been using that DL109 behind the steamers, and very successfully. What smaller engine could i be using?
I happen to have a pretty heavy little switcher engine in my inventory,...an Alco S2 by Atlas,...but could this really substitute for the DL109. (Edited; that may have been a Kato NW2)
WOW, it did a great job. First I put it behind that Bachmann Northern,..
Then behind one of my Mehano mountains,..just plain DC

I was really pleasantly surprised. This little Alco diesel model did a great job. I was pulling 20 car trains up the more difficult ramp side of my viaduct,....4.5% grade. It turns out to have a diecast frame that gives it superb weight.
I went onward to try this little diesel by itself. It couldn't quite make it, but it came close.
I then decided to get one of my Bachmann mountains out for a try. A slight problem arose here due to the Bachmann having a DCC decoder installed, so matching the speeds with the pure DC S2 needed a bit more attention. But it also worked extremely well. (BTW I tried the Bachmann mountain by itself, and was pleasantly surprised at its performance. Double heading these Bachmann mountains will definitely be on my list).
I'm convinced that a likely solution for pushing a lot of my steam engines is disguise one of these Atlas switchers into a aux water tender. Sure would save LOTS of custom efforts at adding extra weights to that variety of steamers.
That was posted over here,
https://forum.mrhmag.com/post/improving-our-steam-engines-performance-12219656?pid=1331406912
Next came this suggestion from the Prof
Prof_Klyzlr Nov 24, 2021
Replacement sideframes
Dear Brian,
The original Atlas S-series switchers were largely metal, and are standouts in haul capacity. Few contemporary switcher models can match them for "out if box" weight and adhesion. The Kato NW2 might go close?
As for "sneaky sideframes", the Atlas S-series were offered with AAR switcher trucks, which are more "visually non-descript" than the Alco "Blunt trucks". AAR trucks also can be mistaken (from a distance) as express baggage trucks under a boxcar, esp in earlier steam and transition eras
Then Rob in Texas added this,..
I just read through this thread and considered some things that will work for me. I will be building a layout with prototypical grades. Nothing above 1.5 percent and minimum radius of 43 inches scale is HO. I have done some experimenting and found the 2-6-6-6 locomotives to be poor pullers compared to the real thing. There have been lots of good points made about ways to improve this. There have been several comments about why it is not needed because most modelers run 12 car trains or similar points.
This was run after using bullfrog snot and I decided it was unacceptable due to its tendency to clean the rails.
I have discovered that all Steam locomotives are not created equal. I added some weight to some Broadway Limited 2-10-4s and found that they became excellent pullers with out traction tires. As to prototype comparisons the 2-6-6-6s were used in the same territory as the 2-10-4s and pulled the same size trains. It seems to me that pairing a 2-10-4 as a pusher or lead engine and a 2-6-6-6 on the opposite end of the train would be the path of least resistance to sending 100 car hopper trains over the railroad with out issue. The prototype would send 160 car trains over the line with either locomotive unassisted. Another strong puller is their 2-8-8-2 model. A while back they loaded some flat cars with real bricks to demonstrate their pulling power. One of my fellow club members commented that some of those bricks were chipped....
Point I am making is there is more than one way to skin the cat. A weaker pulling model can be augmented by a stronger locomotive. If the train length is long enough the coupler slack will run in and out between the locomotives as each shoulders a different portion of the load and it changes due to the dynamics of the rail line.
Another alternative is the diesel locomotive in the tender shell or a cistern. I am inclined to try this with some models that might not be up to the grade and finding something like an RS1 from Atlas and stuffing it into a 3D printed shell. It might mean adding water bottles to trains that did not normally have them. The advantage is that 2-8-2 might then look good pulling that longer train on the layout and have a much easier time doing so. The mechanism would likely last a lot longer as well.
So the solutions for me add weight if it will work. If it will not work then I will add power in the form of another locomotive, or a powered water car.
How could I ignore these suggestions, and my own experimentation?? I was off on a quest to find the best 'pusher-helper' chassis I might find,.... that already existed,....and a way to disguise it.